1. Field of the Invention
The invention relates to a semiconductor device having metal gate and a manufacturing method thereof, and more particularly, to a semiconductor device having metal gate and a manufacturing method capable of avoiding gate-to-contact short (hereinafter abbreviated as GC short) issue.
2. Description of the Prior Art
With a trend toward scaling down the size of the semiconductor device, work function metals are used to replace the conventional polysilicon gate to be the control electrode that competent to the high dielectric constant (herein after abbreviated as high-k) gate dielectric layer. The conventional metal gate methods are categorized into the gate-first process and the gate-last process. Among the two main processes, the gate-last process is able to avoid processes of high thermal budget and to provide wider material choices for the high-k gate dielectric layer and the metal gate, and thus the gate last process gradually replaces the gate-first process.
In the conventional gate-last process, a dummy gate or a replacement gate is formed on a substrate and followed by steps of forming a conventional metal-oxide semiconductor (hereinafter abbreviated as MOS) semiconductor device. Subsequently, the dummy/replacement gate is removed to form a gate trench. Then the gate trench is filled up with work function metals required by different conductivity types. Subsequently, contact plugs and interconnections are built and thus integrated circuits (ICs) are constructed. It is noteworthy that during forming contact openings, which expose the substrate, in the interlayer dielectric (hereinafter abbreviated as ILD) layer, metal gates are often exposed because of misalignment or because the huge vertical deviation between the ILD layer on the substrate and the ILD layer on the metal gate. Eventually, conduct material filling up the contact openings contacts the exposed metal gate, the so-called gate-to-contact (GC) short issue not only adversely impacts IC performance but also become one of the major reason that limiting the process window.